Introduce the basics through entertainment. Children don't want to think that they are working when they are not in school, so introduce them to English by showing them English cartoons with subtitles (if they can read), music CDs, coloring and activity books with words that you read to them, and picture books designed specifically to teach vocabulary through images.
Adopt a method. Once the basic vocabulary and greetings are established and absorbed by the child, you must adopt a method in order to continue lessons in a progression. Methods are per-determined lessons outlined in textbooks or computer learning programs. The book or software lead the learner through a progressive level just as a teacher would in a classroom. You can find children's language textbooks at large bookstores or through Internet bookstores such as Amazon.com or Barnes and Noble. Once you have a methodology book, it is up to you to enforce that your child work at it for a designated period of time each day.
Speak with your child's teacher. Often elementary school teachers will have advice and resources to lend you for helping you teach a language at home. Teachers may also be able to point you towards other parents who are teaching their children additional subjects at home.
Introduce your child to English-speaking cultures. Provide her with books, movies, magazines, television shows, music and newspapers. The more she is exposed to the English language, the more she will learn. Learning at home must be fun and therefore cannot revolve solely around textbook learning.
Speak English at home. Your child will not learn unless he is in an environment that encourages him to speak and practice. Even if he doesn't understand, say everything in English and then repeat in the language he is accustomed to. Fluency in a language is obtained through immersion, and the only way to immerse in a home setting is to conduct your daily life activities in English.
Encourage and praise your child's progress. Tell your child how well she is doing with her lessons when you hear her offer up an English sentence all on her own. Children learn best in the home through positive encouragement.